This invention relates generally to systems and methods for treating liquids carrying suspended or dissolved solids and more particularly to separating the solids from the liquid in order to recover dry solids and/or reusable or potable water.
Membrane treatment processes such as reverse osmosis and thermal treatment processes such as multi-stage distillation are commonly used throughout the world for reducing dissolved salts in a water supply source such as seawater in order to produce potable water. Industrial wastewater is also commonly treated with these processes prior to disposal. The two aforementioned processes become increasingly less efficient as the dissolved salt concentration in the water to be treated becomes higher. In the case of seawater, the recovery efficiency of the two processes typically ranges between 35 to 50 percent. As one example, at a 50 percent recovery capability, only 50 gallons of purified water can be recovered out of every 100 gallons of raw saltwater treated. This particular feature associated with current desalination technologies has become an increasing environmentally related problem because of the need to dispose of the concentrate, i.e., the portion of the process water that remains after producing the distilled or product water. The disposal of this concentrate is capable of causing extreme environmental damage to the aquatic life in the receiving body of water.
The dissolved salt concentration in water can be a limiting factor as to the ability of membrane or thermal distillation processes to treat the water. These two types of processes have demonstrated their ability to feasibly treat seawater having dissolved salt concentrations not much greater than 40,000 mg/l. There are numerous industrially produced wastewaters that have dissolved salt concentrations exceeding this level. Furthermore, reverse osmosis processes require electrical energy, and the electrical energy requirement generally becomes greater as the salinity of the water to be treated increases. Thus, the energy cost of reverse osmosis desalination processes is greater for high salinity liquids.
The use of reverse osmosis membrane technology for the treatment of brackish water, seawater supply sources, and industrial wastewaters continues to grow rapidly. Despite the advances made in improving the membranes, they are still subject to biological and chemical fouling as well as a requirement of periodic cleaning and replacement.
Accordingly, there is a need for a system and method capable of economically treating saltwater and wastewater having unacceptable levels of dissolved salt concentrations to recover dry solids and/or reusable water. It is also desirable to be able to treat feedwater having extremely high salt concentration, such as industrial waters associated with the meat processing industry, oil well production water, and concentrate from reverse osmosis plants.